The present invention relates generally to voltage monitoring systems for use in high voltage alternating current power distribution systems, and more particularly, to a voltage monitoring system which mounts on a conventional test point terminal in the power distribution system to control switching functions in the system.
Frequently, in power distribution systems, it is necessary to verify the presence of an operating voltage on a circuit before that circuit is connected into the system. For example, where a load is to be transferred from an existing source to a new source, a switching control circuit prevents the transfer until the presence of voltage in the new source is confirmed. Preferably, to avoid electrical isolation problems attendant with direct connection to a high voltage circuit, verification of the voltage level in the new source is accomplished without direct connection to the monitored circuit. Furthermore, the verification is preferably made without the use of additional connecting circuitry, since this adds to the cost of the installation and precludes future circuit changes. The present invention provides a voltage monitoring system which meets these requirements by providing a system which mounts on a conventional test point of the type commonly used in power distribution systems.
Often cables used to carry alternating current at high voltage levels in power generating and distribution systems are connected to transformers and other system components by means of plug-in connectors which attach to terminals on the component. Connectors of this type often provide one or more test points for capacitively coupling test or circuit condition indicating devices, such as fault indicators, to the conductor of the connector. One such test point mounted fault indicator is described in U.S. Pat. No. 3,906,477 of to the present inventor. Various types of indicator circuits have heretofore been provided for determining whether the conductor is energized by a high voltage current. Examples of such indicator circuits are described in U.S. Pat. Nos. 3,524,178 and 3,328,690. While such indicator circuits provide a means for determining whether the conductor is energized, they do not provide for control of a related switching function.
The present invention provides a voltage monitoring system which mounts on a conventional power system test point, such as provided in an elbow connector, so as to obviate the need for direct connection to the monitored conductor. By reason of the very high impedance of the connection provided at the test point no additional insulating requirements are entailed. The voltage monitoring system utilizes only a detector unit mounted on the test point and a power supply unit connected to the detector unit by a single flexible cable. The sensing threshold of the system is easily set by means of an adjustment on the sensing unit.
Accordingly, it is a general object of the present invention to provide a voltage monitoring system which provides a control effect for controlling external switching or alarm circuitry, and which can be mounted on the test point of an electrical power distribution system.
It is a more specific object of the present invention to provide a test point mounted voltage monitoring system which is compact in construction and economical to construct.